FIG. 1 shows a schematic diagram of a typical fire alarm system. As shown in FIG. 1, in a fire alarm system, a fire alarm control panel 160 is connected to a plurality of fire detectors 170, notification appliances 180, manual alarms 190, etc. distributed in buildings. The fire detectors 170, the notification appliances 180 and the manual alarms 190 are collectively referred to as peripheral devices. The peripheral device is connected to the fire alarm control panel 160 through a wired or wireless network. In the fire alarm system shown in FIG. 1, the notification appliance 180 may, for example, give an audio alarm (for example, by a buzzer or a loudspeaker), or give an observable visual alarm (for example, by using a strobe). For example, a flash visual alarm is particularly suitable for warning people who have hearing disorders, and is also particularly suitable for noisy environments, such as a shopping mall. For different application environments, preferably the light intensities of visual alarms differ accordingly. For example, for a baby's room, the candela setting of the visual alarm shall be relatively low, while a high candela setting is required in a noisy shopping mall. To this end, preferably the notification appliance shall provide, for example, at least four different candela settings of alarm light, for example, 15 candelas, 30 candelas, 75 candelas and 110 candelas, wherein candela is an international light intensity unit, denoted by cd.
In the prior art, typically, the notification appliance uses a xenon lamp as a flash element. A lamp tube filled with xenon is provided in such a typical notification appliance. When the lamp tube is supplied with a high voltage, the xenon inside the lamp tube is ionized and instantaneously conducted on, so as to generate flash with short duration and high intensity. The notification appliance with a xenon lamp is capable of releasing a sufficient intensity of light in a very short period of time. However, for the ionization of xenon inside the lamp tube, it is usually required to apply a voltage of several thousand volts as a trigger voltage to the lamp tube. Adjusting the trigger voltage applied to the xenon lamp tube can produce different levels of light intensity accordingly.
Another typical notification appliance is a notification appliance using a light emission diode (LED) as a flash element. The core of the LED is a semiconductor wafer, including a P-type semiconductor (mainly holes) and N-type semiconductor (mainly electrons), with a P-N junction being formed between the two semiconductors. When the driving current is flowing through the P-N junction on the wafer, the electrons will be pushed to a P zone where the electrons are combined with the holes and then generate energy in the form of photons. As compared with the xenon lamp, the LED lamp needs a lower drive voltage, has a higher luminous efficiency, and is energy-saving and environmentally friendly, but correspondingly has limited luminous intensity. Adjusting the intensity of the drive current flowing through the LED can achieve different levels of light intensity.